1. Field of the Invention
The present invention relates to an improved architecture for monopulse active aperture arrays; specifically, where a single set of adjustments in the radar system transmit-receive module can simultaneously compensate for errors in both the Sum (S) and Difference (D) beams.
The typical active aperture array architecture in the receive mode can error correct only in the Sum or Difference networks and it cannot correct both networks simultaneously. Further, the typical architecture must be of a high operational precision, thereby also being difficult to manufacture.
It is well known that Sum (S) and Difference (D) illuminations are interchangeable with a steered pair of fixed contiguous beams as for example, in the standard monopulse radar comparator. However, to date, Sum and Difference illuminations have not been used to eliminate error differences.
Emerging active aperture systems require low sidelobe, monopulse capability when the radar system is in the receive mode. A pattern of a typical monopulse beam set, transmitting at 3.00 GHz has for example, 36 elements spaced apart 7.0561 cm (2.7780 inches) with a Sum efficiency of -1.33 dB and a Difference efficiency of -3.15 dB. Utilizing the phase of the Sum beam as a reference we define zero degrees of phase. The Difference beam has two main lobes on either side of the Sum beam peak. One lobe has a pattern phase of zero degrees and the other lobe has a phase of 180 degrees. The improved angular resolution with a monopulse beam set is obtained by the Sum Difference ratio. The amplitude and phase illumination functions for this typical beam set would have a Sum illumination of 0 degrees and a Difference illumination phase which is antisymmetric with one-half being set to 90 degrees and the other half set to -90 degrees. The Sum and the Difference illumination tapers are in phase quadrature. Further, there would be very little correspondence between the two illumination functions.
The problem to be solved then, is to provide a high precision error compensation system that can error correct both the Sum and Difference beams simultaneously, and to design an array architecture capable of forming a monopulse beam set which does not rely on complex beamforming networks.
It is desirable to design a beamforming architecture for a monopulse active array incorporating a commonalty in the manifolding, where a single set of amplitude and phase adjustments in the Transmit/Receive modules steer the beams and compensate for errors in the Sum and Difference manifolds.